SOIL Questions

Where is the soil data coming from?

We use both SSURGO and Stasgo soil data from http://soils.usda.gov/survey/geography/ssurgo/

Why only Silt,Clay, Organic Matter and Bulk Density Percentages?

Soil hydraulic properties such as hydraulic conductivity, porosity etc. were estimated from the SSURGO soil texture properties (sand, silt, clay fractions and the bulk density) using pedotransfer functions. Wösten, J.H.M., Pachepsky, Y., Rawls, W.J., 2001. Pedotransfer functions: bridging the gap between available basic soil data and missing soil hydraulic characteristics. J. Hydrol., 251, pp. 123–150.

For further details refer to:   A DISTRIBUTED HYDROLOGIC MODELING SYSTEM: FRAMEWORK FOR DISCOVERY AND MANAGEMENT OF WATER RESOURCES A Dissertation in Civil Engineering by Gopal Bhatt

Do you have other soil variables? UPDATE May 2014

Yes, but at present we are not making these available for SSURGO. Please either contact us, or visit http://soils.usda.gov/survey/geography/ssurgo/ to access the original datasets. USDA provide tutorials on how to access the soil data and prepare for your research.

However!  We now package gSSURGO soils at HUC-12 scale with the majority of variables made available by USDA (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/home/?cid=nrcs142p2_053628). For further information about the variables , visit http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/home/?cid=nrcs142p2_053631

Some MUKEYs are missing from the soil text file, why?

Some of the reasons include: soil beneath rivers/streams and the data is simply missing. Rather than removing these polygons, we decidied to leave them there so we can eventually update the values and/or have users help us determine values. One possible strategy is to assign values by averaging between neighboring shapes. However, we decidied to leave the data as is that was collected from USDA , so end users can use their own strategy to fill in missing values. To find and replace these values is not a simple task as the SSurgo databases contain more than 300 million polygons and there are 1000's of fields. 

Geology Questions

Isn't the geology file identical to the soil file?

At present we use the spatial distribution from the soil files to assign Vertical saturated hydraulic conductivity in the the geology file. We are working with geological scientists to access national geological datasets to use in future versions of Hydroterre.